The invention provides a fuel supply system for a two cycle internal combustion engine, including an auxiliary fuel enrichment system for preventing knock, and for enhancing operation when the engine is cold.
The auxiliary fuel enrichment system includes a first fuel line connected from the fuel pump to a continuously cyclable control valve, a second fuel line connected from the valve to metering restriction orifice structure, and a third fuel line connected from the orifice structure to the engine intake manifold for supplying fuel to the crankcase. The restriction orifice structure lowers the fuel pressure in the third fuel line to reduce the chance of fuel leakage at the intake manifold, and reduces fuel pressure fluctuations in the third fuel line otherwise due to cycling of the control valve between ON and OFF states.
The control valve is preferably a solenoid controlled by a variable duty cycle oscillator between ON and OFF states. The oscillator may be controlled by knock detection circuitry and/or temperature sensing circuitry.